About the isometric holds... do you mean like in a cable machine, standing, holding the cable to my side and not letting it twist me?

Exactly. Same general concept of the plank, as in holding the body rigid against resistance, only this is working against a rotary/twisting force versus simply gravity. While you are rehabbing, you would be best off to have someone hand you the cable in your "working position" rather than you having to twist to get it into position. This is not a max effort exercise.